Chapter 15 Frequencies and Distributions Flashcards
Distribution
Shape and spread of data sets/populations
Frequency
How often a certain event (e.g. score) occurs
Frequency Distribution
Distribution showing how often certain values occur
Percentile
Point on a measured scale that marks of certain percentages of cases in an ordered data set
Deciles
Points on a measured scale that mark off each 10% of the data set or population
Quartiles
Points on a measured scale that mark the 25th, 50th and 75th percentiles of a distribution
Normal Distribution
Continuous distribution, bell-shaped, symmetrical about its mid-point
z score/value
Alternative term for standard score
Standard Score
Number of standard deviations a particular score is from its sample mean
Sampling Error
Difference between a sample statistic and the true population statistic, usually assumed to be random in origin
Sampling Distribution (of Means)
Theoretical distribution that would be obtained by taking the same statistic from many same size randomly selected samples (e.g. the mean)
Standard Error
Standard deviation of a sampling distribution
Central Limit Theorem
Used in the theoretical estimation of the standard error of a sampling distribution from the standard deviation of a sample
Confidence Intervals/Limits
Estimated limits (e.g. with 95% confidence) to the likely range (interval) within which a population mean lies, based on an estimate from a sample mean and standard error
Skew/Skewed Distributions
Non-normal distributions that have a lot more extreme scores on one side of the mode than on the other
Ceiling Effect
Occurs where measure produces most values near the top of a scale - e.g. easy test
Positively Skewed Distribution
Description of distribution that contains a longer tail of higher values
Floor Effect
Phenomenon where measure produces very many low scores - e.g. difficult test
Kurtosis
Overall shape of a distribution in terms of height and with compared with normal distribution
Platykurtic Distribution
Non-normal distribution that is widely spaced out and low in the centre
Leptokurtic Distribution
Non-normal distribution that is closely bunched in the centre and tail
